Six double-muscled Belgian Blue bulls weighing initially 345 kg (± 16) and fit with ruminal and T- abomasal cannulas receive the same diet consisting of concentrates and wheat straw. The diet is given in ... [more ▼]

Six double-muscled Belgian Blue bulls weighing initially 345 kg (± 16) and fit with ruminal and T- abomasal cannulas receive the same diet consisting of concentrates and wheat straw. The diet is given in three different ways with the aim to creating three durations (0, 12 and 24 hours) of imbalance between energy and nitrogen supplies for the microorganisms in the rumen. OM, N and NDF ingest by bulls for each duration are not significantly different (p > 0.05). The same observation is made for faecal digestibility of OM, N and NDF. Nitrogen retention is not significantly influenced (p > 0.05) by duration of imbalance. The mean of N retention is 57.4 g / d. Partial results for ruminal digestibility show that the different durations have no effect to ruminal digestibility of OM and NDF. Measurement of concentration of urea in blood with serial punctions show that recycling of urea in blood and liver is mechanism able to damp down variations of ruminal ammonia concentrations. This first results show that duration of imbalance between energy and nitrogen supplies for the microorganisms in the rumen does not influence digestibility and N utilization by animal. Cellulolytic activity (measured by fibre digestibility) of microorganisms is not change. [less ▲]